Coils are commonly used as inductor elements in electronic circuits. The coils consist of wire bent to form a series of spaced loops. In high frequency applications, such as radio frequency broadcasting, cable television, cellular phones and other communications technology, air-wound coils are often surface mounted on circuit boards.
Circuit boards are commonly produced by forming wiring that extends on the surface and through holes in a sheet of fiberglass. The wiring includes pads for attaching components to the board. Solder paste is deposited on the pads and then terminals of the components are positioned on the solder paste. Then the assembly is heated sufficient to melt particles of metal in the solder paste to form solder alloy connections between the pads and the component terminals.
A pick-and-place machine is used to place the components onto the wiring substrate. Wiring substrates and components are fed into the machine and a head picks-up the components and places them at component sites on the board. Typically the solder paste is deposited on pads at the component site before the board is fed into the machine. The head includes either a vacuum probe or a mechanical gripper to pick-up, position, and release the components at the sites.
Generally, the position of a coil is not nearly as critical as the positioning of other common components on the circuit board substrate and grippers can place such coil components onto circuit boards without the need for a vision system. Since the surface of uncoated air-wound coils has openings, common vacuum probes can not be used to pick-up the coil components. Thus, mechanical grippers are typically used for placing air-wound coils. However, it is well known to coat the coils of an air-wound coil with a layer of epoxy to allow the coils to be handled using a vacuum probe. In some applications the coils can not be covered with epoxy because the spacing between the loops must be adjusted for tuning the coil and/or circuit of the circuit board. In such a case, uncoated coils are placed on the circuit board using a gripping head.